Method of refining oil with a solvent



Sept l1, 1951 G. B. ARNOLD ET AL METHOD OF REFINING OIL WITH A SOLVENTFiled Feb. 28, 1948 Nw hmm,

T To ENE V5 Patented Sept. 11,` 1951 METHOD F OIL WITH A VENT George B.Arnold, Glenham, and William E. Skelton, Beacon, N. Y., assignors to TheTexas Company, New York, N. Y., a corporation of Delaware ApplicationFebruary 28, 1948, Serial No. 11,988

6 Claims.

This invention relates to a method of refining oil with a solvent liquidwhich is at least partially miscible with water at ordinarytemperatures, and particularly relates to the recovery of the solventfrom the oil by azeotropic distillation.

In accordance with the invention, a relatively low boiling feed oil,such as kerosene or gas oil,

is extracted with a selective solvent, such as furfural, underconditions effective to form extract and raflnate phases respectively.The raiinate phase comprises non-aromatic or relatively insolubleconstituents of the oil mixed with a small proportion of the solvent,while the extract phase comprises the relatively aromatic and naphthenicconstituents oi the oil dissolved in the main body of solvent.

The extract and rafnate phases are separately subjected to distillationin the presence of water vapor and an added quantity of low boiling oilso as to effect separation of solvent from oil. It is contemplatedsupplying suillcient steam or water. as well-as added oil, to thefractionating zones to form ternary water-oil-solvent azeotropes withall, or substantially all, of the solvent present in the extract andrailinate phase mixtures. The added oil has a boiling temperatureintermediate the boiling temperatures of the solvent and water. Thisadded oil may be a fraction of the oil produced by the treatment, or maybe obtained from an outside source.

The resulting distillates are cooled and condensed and then subjected tosettling to form oil-rich, water-rich and solvent-rich liquid layers,respectively. The oil-rich liquid comprising added oil and small amountsoi solvent and water is removed and recycled to the azeotropicdistillation zones as will be described with reference to the drawing.

The solvent-rich liquid comprising solvent and a small amount ofdissolved water and oil is removed and recycled to the extraction zone.The water-rich liquid comprising water and a small amount of solvent isremoved. part being recycled as reux to the fractionating zone, and theremainder subjected to fractional distillation to recover the residualsolvent, the recovered solvent being returned to the extraction tower.

The invention is particularly useful in connection with the solventrefining or extraction of hydrocarbon oilsv boiling in thei'sametem-f`v4 perature range as the solvent or higher boiling than thesolvent, and where the difference in boiling temperature between thesolvent and the lowest honing constituents oi the oil ranges from (Cl.E36-14.48)

several degrees up to about F. 1n other words, the invention is usefulin connection withthe treatment of oils wherein 'the difference betweenthe initial true boiling point of the oil and the boiling temperature ofthe solvent is usually less than about '75 F. Where the difference issubstantially greater than this, no particular problem exists ineiecting recovery of the solvent from the oil by conventionaldistillation methods.

An essential feature of the invention involves the addition to thedistillation zone or zones of a substantial quantity of oil boilingbetween the boiling temperature of water and that of the solventemployed. For example, in the case of extraction with furfural, whichboils at about 322 F., it is contemplated adding to the distillationzone or zones oil boiling within the range about 212 to 320 F. Any`petroleum fraction boiling in this range may be used, although aparafnic fraction is preferable since paraiilns appear to azeotropebetter than aromatlcs. Hydrocarbons such as hexane, heptane, octane andthe like, or mixtures thereof may be used 'as the added substance. Thepurpose of this added oil is to form an azeotrope of increased oilcontent and decreased water content, so that the distillation of theazeotrope from the feed mixture can be effected with greater economy inheat requirements. I

It has been observed that the ternary azeotrope obtained by distilling,in the presence of steam, the raffinate phase resulting from furi'uralextraction of a gas oil having an initial A. S. T. M. boiling point ofabout 458 F. will contain approximately 12% oil, 21% solvent, and 67%Water. On the other hand, the ternary azeotrope obtained by steamdistillation of the raiiinate phase produced by furfural extraction ofkerosene having an initial A. S. T. M. boiling point of about 322 F.contains approximately 33% oil, 21% solvent, and 46% water by volume. Itwill be understood, of course, that the true boiling point ofhydrocarbon mixture is usually' about to 100 F. lower than the A. S. T.M. value.

Thus, it is seen that when the A. S. T. M. inltial yboilinglipoint ofthe oil is about 136 higher than qthe solvent, theternary azeotropecontains a much larger proportion of water thanwhere the A. S. T.' M.initialboiling point is only af "few l.degrees higher than the solventboiling temperature.

In order to illustrate the invention in more detail, reference will nowbe made to the accompanying drawing comprising a flow diagram of theprocess as applied to the treatment of a cycle gas oil produced in thecatalytic cracking of mineral oil and having an A. S. T. M. boilingrange as follows:

I B. P. 458 5% 484 494 5% 530 End Point 622 through a pipe 4. Thesolvent comprises furfural and minor amounts of water and oil as aresult of previous use in the process. It may contain about 15% oil and3% water by volume. The solvent is introduced to the tower in theproportion of about one volume to two volumes of feed oil. Thetemperatures of the entering streams of oil and solvent are regulated,so that the temperature at the bottom of the tower is maintained atabout 100 F. while the temperature at the top is maintained at about 150F.

Under these conditions, extract and raiflnate phases are formed. Theraiilnate phase comprises ol amounting to from about 60 to 80% by volumeof the feed oil. The raiiinate phase is continuously removed from theupper portion of the tower through a pipe 5 and heat exchanger Ii to afractionator 1. A parafiimic hydrocarbon, or a fraction of the railinateoil boiling below 300 F. is injected in the rafllnate phase stream froma pipe I 4 to which reference will be made later.

Heat may be supplied to the bottom of the fractionator either with opensteam, a closed heating coil, or a combination of both. As will bementioned later, provision is made for supplying reflux liquid to thetop of the tower. Suflicient water is introduced to the tower either inthe form of steam or water reflux or both to form the ternary-water-oilfurfural azeotrope with all of the furfural present in the raffinatephase feed. The top of this tower is maintained at a temperature ofabout 205 to 250 F., and the bottom at a temperature of about 250 to 400F. so that the solvent is completely, or substantially completely,distilled from the raiiinate oil. the solvent-free oil being dischargedthrough a pipe 8.

The distillate comprising solvent, water and oil is removed through pipe9 into a condenser I0 and then to a settling chamber II. The settler ismaintained at a temperature of about '70 to 150 F.. and the condensateseparates into oilrich, water-rich and solvent-rich liquid layers,respectively. These layers have the following approximate composition:

The oil-rich liquid layer amounting to about 35% of the mixture passinginto the settler is continuously drawn off through a pipe I2, branch`vipes I3 and I4 through which it is conducted to pipe 5 for injectioninto fresh railinate phase 4 owing into the fractionator 1. Thisoil-rich phase is injected into the rafiinate phase in the proportion ofabout rs to l/2 volumes per volume of rafiinate phase. This injected oilcomprises the added oil added to the railinate phase mixture for thepurpose of obtaining a ternary azeotrope of decreased water content.This added oil may be added initially to the system from a source notshown through pipe I5, and any makeup required to compensate for lossesduring operation may be added through pipe I5.

The solvent-rich liquid is continuously drawn off from the settler I Ithrough pipe 20 and returned to\ the upper portion of the extractiontower 3. Make-up solvent may be added from an outside source throughpipe 2I.

Water-rich liquid is drawn off through pipe 25. and at least a portionthereof diverted through pipe 26 for recycling to the top of thefractionator 1 as refiux liquid. The non-recycled portion is drawn oithrough pipe 21 to pipe 28 through which it is conducted to afractionator 29 for the purpose of stripping residual solvent therefrom.The resulting distillate is conducted through pipe 3|, condenser 32 tosettler 33 wherein separation into water and solvent layers occurs. Thewater layer is recycled to the fractionator, and the solvent layer isdrawn off through pipe 35 for return to the extraction tower 3.

The extract phase is drawn off from the bottom of the lower 3 throughpipe 40 to a fractionator 42 similar to fractionator 1. Added oilsimilar to that obtained through pipe I5, or a fraction of the extractoil product boiling below 300 F. may be injected from pipe I5A into theextract phase in the proportion of about l to 3 volumes per volume ofextract phase.l The fractionator 42 is also provided with means forsupplying heat to the bottom thereof either in the form of open steam ora closed heating coil or both, provision being made also for theintroduction of reflux liquid. Water is injected into the fractionatorto form a ternary furfuraloil-water-azeotrope with a minor portion ofthe extract oil. This azeotrope is thus removed as a distillate throughpipe 43 and condenser 44 to a settling chamber 45 wherein it separatesinto oilrich, water-rich and solvent-rich liquid layers, respectively,each having a composition of approximately the same as those formed inthe settler II. The oil-rich liquid containing added oil is drawn offthrough pipe 46, pipe 41 and pipe 48 through which it is injected intothe stream of extract phase entering the fractionator 42.

The solvent-rich liquid is drawn oil from the settler through pipe 50and returned through pipe 5I to the extraction tower 3.

The water-rich liquid is drawn oil' from the settler 45 through pipe 53and diverted in part through pipe 54 as reflux to the fractionator 42.The remainder of this liquid is conducted to pipe 28' for treatment inthe fractionator 29.

As indicated in the drawing, provision is made for conducting oil-richliquid from either settler II or settler 45 to either of thefractionators 1 and 42. Thus, oil-rich liquid from pipe I2 can i bediverted through pipe I2A communicating with pipe 48. On the other hand,oil-rich liquid from pipe 41 can be diverted through pipe 41A forpassage to the fractionator 1. This arrangement is feasible where thelow boiling oils used in both fractionators 1 and 42 are of the samephysical character; otherwise, added oils of dif-A ferent character maybe used for azeotrope for-l mation in each tower. Provision may alsobomade for discharging oil-rich liquid from each settler.

The raiiinate oil discharged through pipe l will amount to about 60-70%of the feed oil entering through pipe I and will have the followingcharacteristics:

,The extract oil discharged from the fractionator 42 through pipe 60will amount to about {t0-40% of the feed oil and will have the followingcharacteristics: l

'A'. P. I. Gravity 11.9 A. S. T. M. Distllatz'on v Degrees F. I. B. P450 515 50% 542 90% 614 End Point 658 While the treatment of gas oil hasbeen specifically referred to, nevertheless, the process is applicableto the treatment of other types of oil and also to the treatment ofkerosene, the lowest boiling constituents of which may have a. trueboiling point approximating or higher than that of the solvent used. Ingeneral, the invention has application to the treatment of hydrocarbonmixtures having an A. S. T. M. initial boiling temperature within therange about 350 to 500 F. and having an end boiling point ranging fromabout 400 to 650 F. It is contemplated that the invention hasapplication to the treatment of oils derived from animal and vegetablesources. Specific conditions of temperature and solvent dosage may varyfrom those specifically mentioned, depending upon the character of thefeed oil undergoing treatment and the degree of fractional separationdesired.

The invention is particularly concerned with the use of relatively highboiling organic solvent liquids which are miscible, at least to someextent, with water, and with which constituents of the'oil feed in thepresence of water form azeotropes. may be used. They may include otherderivaamarga obtained from said extracting zone, a substantial Selectivesolvents other than furfural f tives of the furan group and otheraldehydes such ture of the solvent being less than about 75 F.

and wherein the feed oil is subjected to contact in an extraction zonewith a water-miscible organic solvent liquid, extract and railinate 7phases are formed, said phases separately removed from the extractionzone. each of said quantity of added oil boiling intermediate theboiling temperature of water and the solvent and capable of ternaryazeotrope formation therewith, passing the resulting mixture into asteam distillation column, effecting distillation thereof in thepresence of steam, the amounts of steam and added oil being suillcientto form ternary water-oil-solvent azeotropes with substantially all ofthe solvent present in the removed phase passing to the steamdistillation column',l removing resulting ternary azeotropes as adistillate from said distillation column, said distillate containingsubstantially less water than when the distillation is effected in theabsence of said added oil, separately removing from the distillationzone a residual liquid of product oil substantially completely free fromsolvent, discharging said residual liquid, subjecting said distillate tocondensation, subjecting the resulting condensate to settling in asettling zone at a temperature in the range about to 150 F.. forming insaid settling zone ollrich, water-rich and solvent-rich layers,respectively, withdrawing liquid from each of said layers,'recyclingwithdrawn water-rich liquid as reflux to the upper portion of saidcolumn and recycling withdrawn oil-rich liquid to the lower portion ofsaid distillation column to re-supply said added oil. y

' 2. The method according to claim 1 in which the feed oil to theextraction zone is a hydrocarbon oil boiling -in the range about 350 to650 F.

3.A In the solvent rening of kerosene and light gas oil, the differencebetween the initial true boiling point of the oil and the boilingtemperature of the solvent being less than about F. and wherein thefeedoil is subjected to contact extraction zone with a. water miscibleorganic solvent liquid, extract and raiiinate phases are formed, saidphases separately removed from the extraction zone, each of said phasescomprising oil and solvent, and the removed phases separately treated toremove solvent from the oil for reuse in the extraction zone, the methodof treating said removed phases comprising passing a removed phase asobtained from said extraction zone to the lower portion of a distillingcolumn, introducing steam and an added oil boiling intermediate theboiling 'temperatures of water and said solvent and capable of ternaryazeotropic formation therewith to the lower portion of said column inamounts suilicient to form ternary water-oil-solvent azeotropes withsubstantially all of the solvent present in the removed phase enteringsaid column, removing resulting ternary azeotropesv as a distillate fromsaid column, said distillate containing substantially less water thanwhen the distillation is eifectedin the absence of said added oil,separately removing from the column a residual liquid of product oilsubstantially completely lfree from solvent, discharging said residual`liquid. subjecting said distillate to condensation, subjectingtheresulting condensate to settling in a settling zone at a temperature inthe range about 70 to 150 F., forming in said settling zone oil-rich,water-rich and solvent-rich liquid layers, respectively, withdrawingliquid from each of said layers, recycling withdrawn water-rich liquidas reilux to the upper portion of said column, and recycling withdrawnoil-rich liquid to the lower portionl of said column to supply saidadded oil.

4. In the solvent refining of kerosene and light gas oil with furfuralin an extraction zone thereby forming extract and railinate phasemixtures,

respectively, the method of treating said phases after separate removalfrom the extraction zone comprising passing a removed phase to adistillation column, introducing steam and an added oil boilingintermediate the boiling temperatures of water and furfural andcapableof ternary azeotrope formation therewith to the lower portion of saidcolumn in amounts suflicient to form ternary water-oil-solventazeotropes with substantially all of the solvent present in the phasemixture passing to said column from the extraction zone, removingresulting ternary azeotropes as a distillate from said column, saiddistillate containing substantially less water than when thedistillation is effected in the absence oi' said added oil, separatelyremoving from the distillation column a residual liquid of product oilsubstantially completely free from solvent, discharging said residualliquid, subjecting said distillate to condensation, subjecting theresulting condensate to settling in a settling zone at a temperature inthe range about 70 to 150 F., forming in said settling zone 011-. rich,water-rich and solvent-rich layers, respec-l tively, withdrawing liquidfrom each of said layers. recycling Withdrawn water-rich'liquid 'asreflux to the upper portion of said column, and recycling withdrawnoil-rich liquid to the lower portion of said column to supply said addedoil. 5. The method according to claim 3 in which the feed oil-to theextraction zone is a hydroi-I gbolrvi oil boiling in the range about 350to 6. The method according to claim 3 in which the added oil boils inthe range of about 212 to 320 F.

GEORGE B. ARNOLD. WILLIAM E. SKELTON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,139,240 McFarland Dec. 6, 1938'2,154,189 Weir Apr. 11, 1939 2,154,372 Bosing Apr. 11, 1939 2,168,570Kraft Aug. 8, 1939 2,216,933 Atkins Oct. 8, 1940 2,381,996 Bloomer Aug.14, 1945 2,465,959 Tindall Mar. 29, 1949 2,475,147 Manley July 5, 1949

1. IN THE SOLVENT REFINING OF KEROSENE AND LIGHT GAS OIL, THE DIFFERENCEBETWEEN THE INITIAL TRUE BOILING POINT OF THE OIL AND THE BOILINGTEMPERATURE OF THE SOLVENT BEING LESS THAN ABOUT 75* F. AND WHEREIN THEFEED OIL IS SUBJECTED TO CONTACT IN AN EXTRACTION ZONE WITH AWATER-MISCIBLE ORGANIC SOLVENT LIQUID, EXTRACT AND RAFFINATE PHASES AREFORMED, SAID PHASES SEPARATELY REMOVED FROM THE EXTRACTION ZONE, EACH OFSAID PHASE COMPRISING OIL AND SOLVENT AND THE REMOVED PHASE SEPARATELYTREATED TO RECOVER SOLVENT FROM THE OIL FOR RE-USE IN THE EXTRACTIONZONE, THE METHOD OF TREATING SAID REMOVED PHASES COMPRISING COMMINGLINGWITH A REMOVED PHASE AS OBTAINED FROM SAID EXTRACTING ZONE, ASUBSTANTIAL QUANTITY OF ADDED OIL BOILING INTERMEDIATE THE BOILINGTEMPERATURE OF WATER AND THE SOLVENT AND CAPABLE OF TERNARY AZEOTROPEFORMATION THEREWITH, PASSING THE RESULTING MIXTURE INTO A STEAMDISTILLATION COLUMN, EFFECTING DISTILLATION THEREOF IN THE PRESENCE OFSTEAM, THE AMOUNTS OF STEAM AND ADDED OIL BEING SUFFICIENT TO FORMTERNARY WATER-OIL-SOLVENT AZEOTROPES WITH SUBSTANTIALLY ALL OF THESOLVENT PRESENT IN THE REMOVED PHASE PASSING TO THE STEAM DISTILLATIONCOLUMN, REMOVING RESULTING TERNARY AZEOTROPES AS A DISTILLATE FROM SAIDDISTILLATION COLUMN, SAID DISTILLATE CONTAINING SUBSTANTIALLY LESS WATERTHAN WHEN THE DISTILLATION IS EFFECTED IN THE ABSENCE OF SAID ADDED OIL,SEPARATELY REMOVING FROM THE DISTILLATION ZONE A RESIDUAL LIQUID OFPRODUCT OIL SUBSTANTIALLY COMPLETELY FREE FROM SOLVENT, DISCHARGING SAIDRESIDUAL LIQUID, SUBJECTING SAID DISTILLATE TO CONDENSATION, SUBJECTINGTHE RESULTING CONDENSATE TO SETTLING IN A SETTLING ZONE AT A TEMPERATUREIN THE RANGE ABOUT 70 TO 150* F., FORMING IN SAID SETTLING ZONE OILRICH,WATER-RICH AND SOLVENT-RICH LAYERS, RESPECTIVELY, WITHDRAWING LIQUIDFROM EACH OF SAID LAYERS, RECYCLING WITHDRAWN WATER-RICH LIQUID ASREFLUX TO THE UPPER PORTION OF SAID COLUMN AND RECYCLING WITHDRAWNOIL-RICH LIQUID TO THE LOWER PORTION OF SAID DISTILLATION COLUMN TORE-SUPPLY SAID ADDED OIL.